ESRM 250 CFR 520 Introduction to GIS Raster

ESRM 250 & CFR 520: Introduction to GIS Raster Analysis 1 ESRM 250/CFR 520 Autumn 2009 Phil Hurvitz © Phil Hurvitz, 1999 -2009 1 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 2 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 2 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Raster layer types Raster layer properties Adding raster layers to views Displaying raster layers Examining cell values in raster layers Managing raster layer files © Phil Hurvitz, 1999 -2009 3 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview “Grid” layers are Arc. View's implementation of the basic raster data model. environmental data are represented as “grid” raster layers (image from ESRI) © Phil Hurvitz, 1999 -2009 4 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are Arc. View's implementation of the basic raster data model. rectangular tessellation of © Phil Hurvitz, 1999 -2009 square cells 5 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are theoretically different from image layers Grids and images are stored in the same basic (raster) format: a rectangular matrix of cells where each cell has a value Image layers always represent remotely sensed imagery (e. g. , digital orthophoto) Grids typically represent other continuous phenomena (e. g. , slope, salinity) © Phil Hurvitz, 1999 -2009 6 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview All images are rasters. All grids are rasters. NOT all rasters are images or grids rasters grids © Phil Hurvitz, 1999 -2009 images 7 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are different from image layers þ These are image layers reflectance values © Phil Hurvitz, 1999 -2009 8 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are different from image layers þ These are grid layers elevation etc. values © Phil Hurvitz, 1999 -2009 9 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are different from image layers © Phil Hurvitz, 1999 -2009 10 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Grid layers are different from image layers cells have numerical value that represent a numerical variable © Phil Hurvitz, 1999 -2009 11 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Overview Raster layers are suited for representation of phenomena that vary gradually over space e. g. elevation, wind speed, or slope © Phil Hurvitz, 1999 -2009 12 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Raster types Only integer rasters can have layer tables integer (no decimals) floating-point (decimals) © Phil Hurvitz, 1999 -2009 13 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Raster types Only integer rasters can have layer tables will not have a table will have a table © Phil Hurvitz, 1999 -2009 14 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: The spatial analyst All raster layer functionality occurs through the Spatial Analyst extension. Loading of raster layers for analysis þ Raster analysis þ þ Spatial analyst must be enabled to perform raster analysis © Phil Hurvitz, 1999 -2009 15 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Raster layer properties Layer description contains a lot of information © Phil Hurvitz, 1999 -2009 16 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Raster layer properties Layer description contains a lot of information © Phil Hurvitz, 1999 -2009 17 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Raster layer properties Layer description contains a lot of information © Phil Hurvitz, 1999 -2009 18 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Adding raster layers to views Add raster layers in the same way as adding other data sets © Phil Hurvitz, 1999 -2009 19 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Displaying raster layers Usually numerically classified Symbology can be altered like other layers © Phil Hurvitz, 1999 -2009 20 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Examining cell values with histogram Histograms describe structure of data values Y-axis: cell counts in each value class X-axis: values © Phil Hurvitz, 1999 -2009 21 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Examining cell values with identify tool Individual cell values can be identified as with feature data © Phil Hurvitz, 1999 -2009 22 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Examining cell values with queries Integer rasters can be queried in the usual way þ Selected sets/cells shown in cyan © Phil Hurvitz, 1999 -2009 23 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster layers: Managing raster layer data files Raster data sources should always be managed by Arc. Catalog copying þ moving þ renaming þ deleting þ © Phil Hurvitz, 1999 -2009 24 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 26 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties Analysis properties determine spatial properties for all newly created output raster layers Analysis properties: þ þ Working directory Analysis mask Analysis extent Cell size Once set, analysis property values stay set until changed [Settings described below] © Phil Hurvitz, 1999 -2009 27 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: working directory Working directory specifies the default location for new rasters created with the Spatial Analyst Extension © Phil Hurvitz, 1999 -2009 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Analysis extent sets the spatial properties for output of analyses þ Extent is a rectangular area © Phil Hurvitz, 1999 -2009 28 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Analysis extent Be careful about setting extent; it may cause poor raster-to-raster registration © Phil Hurvitz, 1999 -2009 29 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Analysis extent Be careful about setting extent; it may cause poor raster-to-raster registration Use “snap extent to” © Phil Hurvitz, 1999 -2009 29 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Cell size Analysis cell size sets the raster cell size for output of analyses Use consistent cell size for analysis of multiple raster data sets Note: þ þ þ small cells → larger files (-) small cells → longer processing (-), but … small cells → usually greater accuracy (+) © Phil Hurvitz, 1999 -2009 30 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Masking Analysis mask defines “valid data extent” of output rasters A mask can have any shape (whereas analysis extent is always rectangular) © Phil Hurvitz, 1999 -2009 31 of 52

ESRM 250 & CFR 520: Introduction to GIS Setting raster analysis properties: Masking Analysis mask defines “valid data extent” of output rasters “mask_grid” has a specific extent of valid data (in green) output matches the same data extent © Phil Hurvitz, 1999 -2009 32 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 34 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types Local functions Global functions Zonal functions Focal functions © Phil Hurvitz, 1999 -2009 35 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types: Global functions Local functions apply an independent calculation to all input raster cells Each output cell’s value is calculated independently local sine e. g. sin(12) = -0. 537 © Phil Hurvitz, 1999 -2009 36 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types: Global functions apply a calculation considering all cell values the value 3 is calculated by knowing that flow comes from other cells the value 5 is calculated by knowing that flow comes from other cells, cumulatively e. g. flow accumulation © Phil Hurvitz, 1999 -2009 37 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types: Zonal functions apply one calculation to all input raster cells within each zones are defined as a group of cells having the same value © Phil Hurvitz, 1999 -2009 38 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types: Zonal functions apply one calculation to all input raster cells within each zone zonal sum for zone 1: (53 + 57 + 33 + 78 + 31 + 12 + 32 + 9 + 33 + 76) = 423 all cells in zone 1 in the output are given value 423 © Phil Hurvitz, 1999 -2009 39 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster function types: Focal functions apply one calculation to all input raster cells within a “focus” focal mean (27 + 8 + 22 + 16 + 21 + 16 + 44 + 8) / 9 18. 7 The “focal” cell in the output grid is given value 18. 7 © Phil Hurvitz, 1999 -2009 40 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 41 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: calculations across multiple rasters Multi-raster analyses are possible because of spatial registration multiple raster layers share the same X, Y coordinate space cell values are calculated across multiple raster layers to create a single output raster layer © Phil Hurvitz, 1999 -2009 42 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis Analyses are performed using GUI tools Spatial Analyst toolbar > Raster Calculator © Phil Hurvitz, 1999 -2009 43 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis Analyses are performed using GUI tools Arc. Toolbox tools © Phil Hurvitz, 1999 -2009 44 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis Many more raster analyses are available through the Raster Map Algebra syntax, which can be used in the Raster Calculator or custom tools © Phil Hurvitz, 1999 -2009 45 of 52

ESRM 250 & CFR 520: Introduction to GIS Overview Raster layers Setting raster layer and analysis properties Projections and raster layers Raster function types Performing raster analysis Map Algebra © Phil Hurvitz, 1999 -2009 46 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Raster layers may be used in arithmetic expressions in the raster calculator output_data_set = input_raster 1 operator input_raster 2. . . e. g. , slp_dem = slp_raster output © Phil Hurvitz, 1999 -2009 input 1 * dem operator input 2 47 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Raster layers may be used in algebraic functions in the raster calculator output_data_set = function (input_data_set[s]{, arguments}) e. g. , slp_raster = slope (dem, percentrise) output © Phil Hurvitz, 1999 -2009 function input 1 input 2 47 of 52

ESRM 250 & CFR 520: Introduction to GIS Performing raster analysis: Using rasters in math Map algebra is calculated with the Raster Calculator raster layers operator classes expression box © Phil Hurvitz, 1999 -2009 48 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Map Algebra arithmetic: þ þ Calculation = (dem greater than 500 and dem less than 1000 ) Logical (Boolean) criteria © Phil Hurvitz, 1999 -2009 49 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Map Algebra arithmetic: 0 = false 1 = true © Phil Hurvitz, 1999 -2009 50 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Map Algebra function: þ þ Calculation = mosaic([q 1822], [q 1823]) Mosaics two rasters © Phil Hurvitz, 1999 -2009 51 of 52

ESRM 250 & CFR 520: Introduction to GIS Raster analysis: Map algebra (or “How it works”) Map Algebra function: © Phil Hurvitz, 1999 -2009 52 of 52